Office equipment such as printers and copiers, which place images based on digital data onto sheets, such as sheets of paper are well known. In such equipment it is important that the sheet that is to receive the image is properly aligned with the edge of the feed path as well as not skewed so that the image is properly positioned on the sheet. Various types of registration systems to correct for skew and provide for positioning of the side edge of the sheet are know in the art.
One type of lateral registration system involves the use of a two nip differentially driven deskewing system. Such a system can provide lateral registration of the sheet by deskewing (differentially driving the two nips to remove any sensed initial sheet skew) and then deliberately inducing a fixed amount of sheet skew (rotation) with further differential driving, and driving the sheet forward while so skewed, thereby feeding the sheet sideways as well as forwardly, and then removing that induced skew after providing the desired amount of sheet side-shift providing the desired lateral registration position of the sheet edge.
One such system involving lateral registration using two nips includes a single motor driving spaced apart nips. A differential drive system is used for inducing the skew rotation of the sheet. The single motor is operatively connected to at least one of the nips through the differential drive system. The differential drive system provides relative differential angular movement to the spaced apart nips to achieve the desired amount of sheet deskewing movement.
Another type of system is a translating electronic registration (TELER) system. Such a system generally includes three optical sensors, a pair of coaxial independently driven drive rolls, a carriage with a linear drive on which paper drive rolls are mounted, and a microprocessor controller. A blank copy sheet is driven into the nip rolls and moved through the paper path for placement and fusing of an image thereon. The speed of both nip rolls can be controlled to effect skew alignment and longitudinal registration. The nip rollers are mounted on a carriage movable transversely with respect to the feed path. A sensor system controls positioning of the carriage to achieve the desired top edge or a lateral positioning of the sheet. Independent control of nip roll drive and carriage translation provides simultaneous alignment in lateral and longitudinal directions.
Examples of these systems may be found in U.S. Pat. No. 4,971,304 to Lofthus; U.S. Pat. No. 5,169,150 to Wenthe, Jr.; U.S. Pat. No. 5,219,159 to Malahowski et al; U.S. Pat. No. 5,278,624 to Kamprath et al; U.S. Pat. No. 5,794,176 to Milillo; U.S. Pat. No. 6,137,989 to Quesnel; U.S. Pat. No. 6,181,153 to Richards et al; U.S. Pat. No. 6,533,268 to Williams et al; and U.S. Pat. No. 6,866,260 to Lloyd et al. The disclosure of each of these patents is incorporated herein by reference in its entirety.
In U.S. Pat. Nos. 6,168,153 to Richards et al, 6,173,952 to Richards et al and 6,817,609 to Halvonik et al, the disclosure of each of which is incorporated herein by reference in its entirety, there is disclosed a sheet registration system in which the sheet is fed into the nips of a pre-transfer nip assembly unit. That unit feeds the sheet into the downstream receiving device (an image transfer station). Once the sheet has been fed far enough into the image transfer station to the position of the maximum tack point of electrostatic adhesion to the photoreceptor within the image transfer station, the nips of the pre-transfer nip assembly are automatically opened so the photoreceptor will control the sheet at that point. However, there is no relationship shown between the pre-transfer nip assembly unit and the sheet registration system.
The lateral registration systems shown in the above mentioned patents receive a sheet at its input or upstream end which may be misregistered and deliver it registered to a downstream receiving device for further processing. In moving through the registration system from input to output, the registration system typically moves the sheet in 2 or 3 degrees of freedom, (x, y, and theta, also known as process, lateral and skew) to achieve registration before the sheet lead edge is captured by the downstream receiving device.
A typical registration system must be capable of handling sheets of various lengths. An obvious constraint is that the distance between the output or hand-off location of the registration system and the point of capture of the sheet in the receiving device must be less than the length of the shortest sheet that is to be accommodated by the system. This unnecessarily constrains the length of the registration movement for long heavy-weight sheets that require the largest nip forces and tail wag (lateral swing of the tail edge of the sheet) to correct a given amount of input error as the sheet may become engaged by the receiving device before the registration is complete. This may place some limitations on the range of sheet sizes with which the system may be used.